A liquid sampler set forth in this disclosure is a device for extracting a sample flow from a larger liquid stream. A typical circumstance of use is taking a sample from a crude oil source. The liquid sampler of this disclosure is a device which is provided by the Welker Engineering Company, the sampler being described by various patents including U.S. Pat. No. 4,403,518. The liquid sampler construction utilizes a reciprocating pump rod driven by some type of motor (a diaphragm motor in the preferred embodiment). The lower of the metal rod is normally described as an anvil which works opposite a collection head. The collection head has a cylindrical rubber plug within a surrounding metal sleeve. It is positioned so that the anvil moves relatively against the rubber plug. The rubber plug has a dished region surrounded by a peripheral lip. This lip makes sealing contact and thereby captures fluid within the dished region. As pressure is applied against the rubber plug, the volume of the dished region becomes smaller and disappears. Liquid in that region is forced out of the chamber and flows through a small opening in the anvil. It flows past a spring loaded poppet valve and into a passage for removal for a subsequent use.
The described apparatus has met with great success. It is able to collect minute samples in routine operation with a great variety of liquids and subject to pressure over a wide range. The device has indefinite life in practically all regards except that the resilient plug is subject to failure through resilient fatigue. Interesting, the failure mode is first observed in the resilient plug by the formation of stress cracks or fractures at the center of the dished region. The dished region is more or less in the shape of a hemisphere to provide the chamber which collects the liquid which is subsequently forced out through the poppet valve connected at a small opening in the anvil. The failure normally occurs approximately at the center of the chamber, this being the volume opposite a small opening in the anvil which evacuates liquid flow. Liquid flows from that region into the poppet valve under pressure as the chamber in the resilient plug disappears. The failure is thus immediately adjacent to the small opening which communicates with the poppet valve. It may begin with relatively small stress fractures in the resilient plug but they soon extend and result in catastrophic failure of the resilient plug. The plug then must be replaced.
Replacement is not so difficult but it is difficult to predict when the resilient plug might fail. Thus, the pump device must be inspected periodically to determine whether or not the resilient plug has begun to fail. Since failure is not precisely predictable, periodic servicing of the liquid sampler must be undertaken at no small expense. This is particularly true when the liquid sampler is located at remote or unmanned locations, as for instance in the gathering lines connecting several oil wells with a storage tank battery. It is not uncommon to install this type of device at a tank battery to obtain liquid samples. The samples are necessary so that the collected crude can be periodically tested as a sample. This relates significantly to the value of the crude as well as the specific assay for purposes of post production treatment. While there are many reasons to install such device, it is equally important to assure that it continues to operate successfully without failure. In particular, it is important to assure that the liquid sampler continues to collect samples without failure of the resilient member.
With the foregoing in mind, the present disclosure is directed to an improved resilient plug cooperative with a liquid sampler system. The resilient plug is cylindrical on the exterior and has a top end surrounding peripheral face for contact with the anvil. The plug is centrally dished and has an approximately hemispherical cavity. It is integrally cast about a small metal insert located at the center line of the cylindrical body and therefore at a center line axis through the chamber. The insert is a small disc having a narrow neck and an enlarged root which is surrounded by the cast resilient material to ensure anchoring. It is sufficiently large in diameter to confront the opposite opening in the anvil. This prevents dimpling of the resilient material by extruding into the opening. This thereby prevents stress fractures from building up in the center portion of the resilient plug and markedly changes the life of the device.
While the foregoing sets forth the present invention in summary form, many other objects and advantages will be observed on a review of the detailed description of the present apparatus found below.